The big question I want to ask is this: just because we can live somewhere, should we? It's been asked many times before, in many different ways, with many different answers. But it seems to me that if we're going to continue as a species (feasibility) and not destroy our environment (sustainability) then the answer would be a straightforward no.
Extreme living, my title for this post, doesn't refer to places like Antarctica or the Mojave Desert, where resources essential for life are virtually non-existent. It refers to our tendency to settle and develop any area that is marginally habitable with the assistance of modern infrastructure.
Let's take Houston, Texas for an example. It's a big city. As of the 2008 census it had a population of 2.2 million, not including outlying areas such as Galveston. Yet, it's a singularly unpleasant place to live, and for most residents it would be intolerable without air conditioning. It sits only several feet above sea level, and the water table is literally a few feet below the surface. The humidity is uncomfortably high year-round. When it rains, there is standing water for days. The mosquito population is enormous, and requires pesticide spraying after rainstorms. Fire ant mounds dot the landscape. It is easily threatened by storm surges and hurricanes.
So why is it such an enormous city? The answer is business. It has a large port, and sits in the middle of a rich oil field. From the shores of the city one can see many drilling rigs dotting the Gulf of Mexico. This is the justification for its existence. Once the oil reserves run dry, will the city dry up as well, much as Detroit did when the steel industry disappeared?
Houston at least has a reason to exist, and a lucrative one at that. Lets turn out attention to another city which has a population of 1.5 million. Phoenix, Arizona. This city also owes its existence to air conditioning, as well as the ability to deliver water from far flung sources. For approximately a third of the year the daytime temperatures go above 100 degrees F. The area receives an average of about 8 inches of rain per year. It has little redeeming agricultural value in the current economy due to non-competitive levels of operating costs. It has switched in part to tourism to support the economy, as well as encouraging high tech companies to relocate due to low cost of living.
Despite its continued survival, and even growth, this city requires resources and practices well above and beyond those in more temperate climates. For all intents and purposes, it is a desert settlement. It requires far more water than nature provides to the area, as well as large amounts of electricity for constant cooling of all buildings. Due to the extremely arid climate common food crops cannot be grown locally, thus forcing all food to be brought in from farther afield.
All of this begs the question. Should cities such as these be encouraged? Should we, as responsible and culpable members of our species, voluntarily participate in their existence, despite their overwhelming (and sometimes disproportionate) use of resources? Resources which often are taken from the areas where they naturally occur, and diverted hundreds or even thousands of miles? Can we argue that they are necessary due to population growth, when so many more hospitable areas are left untouched?
Maybe that's the real sticking point. Maybe we need to stop for a moment and question our apparent need to continually increase our population. In other species, nature has checks and balances to constrain a population. With our current level of technology we have managed to remove those checks and balances. It may be that there truly are too many of us, and that this will be the cause of our demise. Because we can is not, and has never been, a valid or logical argument.